The time that patients are mechanically ventilated can be safely reduced by using daily assessments for a patient’s readiness to wean, followed by extubation after a successful spontaneous breathing trial.(1) This method of weaning still results in a reintubation rate of around 10-20%. In the December 2006 issue of the journal of Chest, Frutos-Vivar and colleagues (2) performed an international multicenter study assessing the variables associated with the reintubation of patients that had been extubated after a successful spontaneous breathing trial.
A total of 980 patients from 37 hospitals in eight countries who had been mechanically ventilated for >48 hours were included in the study. Every day patients were assessed for the following readiness-to-wean criteria:
- improvement in the underlying condition that led to respiratory failure
- alert and able to communicate
- core temperature not > 38°C
- no vasoactive drugs (excluding dopamine < 5 µg/kg/min)
- adequate gas exchange, as indicated by a PO2 of at least 60 mm-Hg with an FiO2 of ≤ 0.40 and a PEEP not > 5 cmH2O
Patients that met the criteria for readiness-to-wean were then weaned using one of the following techniques:
- daily trial of spontaneous breathing (SBT) for up to 120 mins using a T-piece, CPAP, flow-by, or pressure support of < 8 cmH2O
- multiple daily SBTs
- gradual reduction of pressure support until a level of ≤ 7 cmH2O
All patients passed a SBT and were extubated. After extubation patients were followed up for the presence of post-extubation respiratory distress. Patients were re-intubated if they met at least one of the following criteria:
- lack of improvement and/or worsening in arterial pH or PCO2
- decreased mental status
- SaO2 decrease to < 85%, despite high FiO2
- lack of improvement in signs of respiratory muscle fatigue
- hypotension, BPsys < 90 mm Hg for 30 mins despite volume loading and vasopressors
- copious secretions that the patient could not clear
Extubation failure occured in 13.4% of patients. Reasons for reintubation were:
- lack of improvement in work of breathing (45%)
- hypoxemia (22%)
- respiratory acidosis (11%)
- retained secretions (10%)
- decreased level of consciousness (6%)
- hypotension (6%)
From all the gather data collected they found that a rapid shallow breathing index (RSBI=f/VT) > 57 breaths/min/L, a positive fluid balance 24 hours prior to extubation, and pneumonia as the cause of mechanical ventilation was associated with reintubation within 72 hours. The RSBI was an independent predictor of extubation failure and a RSBI of > 57 increase the risk of reintubation from 11% to 18%.
Patients in the study that had a positive fluid balance 24 hours before extubation had a higher incidence of reintubation. The study did not collect data on hemodynamic or echocardiograhic measurements so it cannot be said whether the positive fluid balance correlated with ventricular dysfunction. The other variable that was found to be related toreintubation was pneumonia as the need for mechanical ventilation.
The nice thing about this study is its very large sample size and careful analysis. The study also had a reintubation rate that is consistent with many other reports. One possible flaw in the study is that the decision to extubate was not protocolized, the physician in charge made the final decision. So specifically, we don’t know if some of these patients may have had a delay before beingextubated and we do not know why this is. Also, of the patients that required reintubation , very few of them were related to airway protection issues. This may be due to assessments of the patients ability to protect their airway but this was not recorded so we don’t know.
This study does add to our knowledge and understanding of the process of weaning and liberation from mechanical ventilation. Especially in understanding why patients failextubation and how our current tools for assessing the readiness for extubation are not perfect. There is still more room for work to be done in this area but Frutos-Vivar et al have begun to give us a clearer understanding of why patients may fail extubation after a successful spontaneous breathing trial.
(1) MacIntyre NR, Cook DJ, Ely EW, et al. Evidence-based guidelines for weaning and discontinuing ventilatory support. Chest 2001; 120:375S-395S.
(2) Frutos-Vivar F, Ferguson N, Esteban A, et al. Risk factors for extubation failure in patients following a successful spontaneous breathing trial. Chest 2006; 130:1664-1671.
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